1. Field of the Invention:
This invention relates in general to subsea well equipment, and in particular to an apparatus for tying back a wellhead housing located at the sea floor to the surface.
2. Description of the Prior Art:
One type of subsea well employs a wellhead housing located at the sea floor and the production Christmas tree located at the surface on a platform. Large diameter casing will be lowered from the surface down toward the wellhead housing. A tieback connector will connect the wellhead housing to the riser.
One type of tieback connector has a downward facing funnel that slides over the wellhead housing. The tieback connector has a body with a lock nut carried within an axial bore. After the funnel has landed the tieback connector body on the wellhead, a running tool will engage the lock nut and move it downward into the bore of the wellhead housing. Threads are provided in the wellhead housing for receiving external threads on the lock nut. The running tool rotates the lock nut to tighten the threads for pulling the tieback connector tightly against the wellhead housing.
While successful, a possibility exists that the internal threads in the wellhead housing could be damaged during earlier drilling operations. Most wellhead housings have large internal grooves which are used for various purposes. U.S. Pat. No. 4,696,493, Norman Brammer, issued Sept. 29, 1987, shows a tieback connector that utilizes these grooves for connecting the lock nut to the wellhead housing.